There is a need for methods to determine an intended path of travel for a vehicle and to automatically provide steering and braking control to maintain a vehicle on the intended path during braking maneuvers by coupling the road path and the driver's intended path with the need for autonomous braking. The results of the methods herein disclosed maximize velocity reduction during the braking maneuver while maintaining the vehicle on the desired path.
Electronic Stability Control (ESC) is the generic term for systems designed to improve a motor vehicle's handling, particularly at the limits where the driver might lose control of the motor vehicle. See, for example, the Society of Automotive Engineers (SAE) document on “Automotive Stability Enhancement Systems”, publication J2564 (December 2000, June 2004). ESC compares the driver's intended direction in steering and braking inputs to the motor vehicle's response, via lateral acceleration, rotation (yaw) and individual wheel speeds, and then brakes individual front or rear wheels and/or reduces excess engine power as needed to help correct understeer or oversteer. ESC also integrates all-speed traction control which senses drive-wheel slip under acceleration and individually brakes the slipping wheel or wheels, and/or reduces excess engine power until control is regained from a sliding situation. ESC cannot override a car's physical limits. It is a tool to help the driver maintain control. ESC combines anti-lock brakes, traction control and yaw control (yaw is spin around the vertical axis).
ESC systems use several sensors in order to determine the state the driver wants the motor vehicle to be in (i.e., a driver command). Other sensors indicate the actual state of the motor vehicle (i.e., motor vehicle response). The ESC control algorithm compares both states and decides, when necessary, to adjust the dynamic state of the motor vehicle. The sensors used for ESC have to send data at all times in order to detect possible defects as soon as possible. They have to be resistant to possible forms of interference (rain, potholes in the road, etc.). The most important sensors are: 1) steering wheel sensor, used to determine the steering angle the driver wants to take, often based on anisotropic magnetoresistive (AMR) elements; 2) lateral acceleration sensor, used to measure the lateral acceleration of the motor vehicle; 3) yaw sensor, used to measure the yaw angle (rotation) of the motor vehicle, can be compared by the ESC with the data from the steering wheel sensor in order to take a regulating action; and 4) wheel speed sensors used to measure the wheel speeds.
ESC uses, for example, a hydraulic modulator to assure that each wheel receives the correct brake force. A similar modulator is used with anti-lock brake systems (ABS). ABS needs to reduce pressure during braking, only. ESC additionally needs to increase brake pressure in certain situations.
The heart of the ESC system is the electronic control unit (ECU) or electronic control module (ECM), (i.e., motor vehicle controller or microprocessor). Diverse control techniques are embedded in the ECU and often, the same ECU is used for diverse systems at the same time (ABS, traction control, climate control, etc.). The desired motor vehicle state is determined based on the steering wheel angle, its rate of change and the wheel speed. Simultaneously, the yaw sensor measures the actual state. The controller computes the needed brake or acceleration force for each wheel and directs the actuation of, for example, the valves of a hydraulic brake modulator.
Motor vehicles utilizing electronic stability control systems require some means of determination of the driver's intended motor vehicle behavior (i.e., intended motor vehicle path or track). In General Motors' (GM's) StabiliTrak™ system these means are accomplished by the driver command interpreter, as described in U.S. Pat. No. 5,941,919 (issued Aug. 24, 1999), which is incorporated herein by reference in it's' entirety.
Referring now to FIG. 1, the exemplar prior art control structure described in U.S. Pat. No. 5,941,919 is shown. The controller 10 includes command interpreter 12 receiving the various system inputs from various vehicle sensors 14. The command interpreter 12 develops desired yaw rate commands responsive to the various system inputs and a data structure 16 stored in non-volatile memory of controller 10. The data structure 16 has a data subset 18 corresponding to vehicle operation in linear mode and a data subset 20 corresponding to vehicle operation in non-linear mode (e.g., skidding or sliding).
When the vehicle operation is in the linear mode, the command interpreter 12, using data structure subset 18, provides commands to a control block 22 designed to maintain the linear response of the vehicle. For example, when the control according to this system is used to control wheel brakes to affect vehicle yaw control, the commands provided by block 12 do not modify the wheel brake operation while the vehicle is in the linear mode. When the control is used to control a vehicle variable force suspension system, the suspension control is provided to maintain the current driving conditions, and not to induce a change in understeer or oversteer.
When the vehicle operation is in the non-linear region, the command interpreter 12, using data structure subset 20, provides commands to the control block 22 commanding a yaw rate linearly responsive to the vehicle steering wheel input. Block 22 uses the command generated at block 12 to control one or more vehicle chassis systems, such as controllable suspension actuators, represented by block 24 and/or brakes, represented by block 26 to bring the actual vehicle yaw into a linear relationship with vehicle steering wheel angle. This control thus maintains the yaw response of the vehicle linear with respect to the steering wheel input even when the vehicle is operating in its nonlinear performance region.
Also, collision preparation systems (CPS) are known in the art and are exemplified by U.S. Pat. No. 7,280,902 which discloses a motor vehicle deceleration control apparatus; U.S. Pat. No. 7,035,735 which discloses a method and device for automatically triggering a deceleration of a motor vehicle; and U.S. Patent Application Publication 2004/0254729 which discloses a pre-collision assessment of potential collision severity for motor vehicles.
U.S. Pat. No. 6,084,508, issued Jul. 4, 2000, the disclosure of which patent is hereby herein incorporated by reference. U.S. Pat. No. 6,084,508 discloses a collision preparation system which provides autonomous braking in certain situations. The method and arrangement for emergency braking of a vehicle, include a detection system on the vehicle which detects obstacles located in or near the direction of motion of the vehicle and generates corresponding data, sensors on the vehicle which generate data representing characteristic parameters of the condition of the vehicle, and an evaluating unit which determines, from the data on the obstacles and the parameters of the condition of the vehicle, target values for controlling the motion of the vehicle and, only upon determining that an impending collision of the vehicle with an obstacle is no longer avoidable by any action on the vehicle by steering or braking, triggers an autonomous emergency braking for rapid deceleration of the vehicle.
As described in U.S. Pat. No. 8,126,626, during an autonomous braking event as a result of actuation of a collision preparation system (CPS), the driver intended travel path and the actual motor vehicle travel paths are monitored. In the event that the vehicle departs from the driver intended motor vehicle travel path, the braking is lessened, so as to attempt to follow the motor vehicle travel path intended by the driver. However, the previous designs are strictly reactive. U.S. Pat. No. 8,126,626 was issued on Feb. 28, 2012 and is incorporated herein in its entirety.
Inputs from various sensors 14 and other data sources of the motor vehicle are provided to the stability controller 10. The stability controller 10 includes a command interpreter 12. The stability controller 10 utilizes the command interpreter 12 and the control commands block 22 to control operation of the braking system 26 in the manner described pursuant to U.S. Pat. Nos. 5,941,919 and 8,126,626.
The CPS braking adjustment controller 224 has provided to it, via a data line 226, the driver braking request, the yaw rate and/or other data providing actual motor vehicle travel path information, and the steering wheel position and/or other data providing the driver intended motor vehicle travel path information, are all available from the command interpreter 12 (although such an arrangement is exemplary and not intended to be limiting) and the CPS braking adjustment controller 224 further has available to it, via a data line 228, the activation status of the CPS 210 indicative of the autonomous braking status and the braking request of the CPS. The CPS braking adjustment controller 224 sends a braking reduction signal, via data line 230, to the braking system 26 in the event there is a detected difference (in practice, at least a predetermined small difference) between the driver intended motor vehicle travel path as compared to the actual motor vehicle travel path, wherein, preferably, the driver braking request does not exceed the CPS braking request.
However, this control action only seeks to correct the path by reducing the Collision Preparation System braking. The amount of velocity reduction by the braking system (the goal of the Collision Preparation System) is diminished with the expense of maintaining the intended path. Accordingly, what is needed in the art is a motor vehicle travel path control which monitors, during an autonomous braking event, the actual motor vehicle travel path in relation to the driver intended motor vehicle travel path and has the ability to minimize the difference between the two by generating a corrective yaw moment. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.